ASA S3.35-2004

This standard describes techniques used to measure hearing aids under simulated conditions of real ear use. The need for such a standard arises from the importance of including the acoustical variations in the performance data that are caused when hearing aids are worn. For example, the diffraction of the body and head of a hearing aid wearer on incident sound can significantly change the input sound pressure to a hearing aid microphone. For the purpose of these measurements, a suitable manikin and ear simulator are used to represent a typical hearing aid wearer. Acoustical requirements of the test space as well as how the manikin is positioned with respect to the sound source are given. Two methods are presented by which to control the level of the incident sound field at the location of the hearing aid on the manikin during the testing. Procedures are provided to obtain the insertion gain, or the amount by which the hearing aid changes the eardrum sound pressure in the ear simulator of the manikin relative to that in the unaided condition. Procedures are also provided to obtain the directional response of the manikin as a function of azimuth and elevation of the sound source, with and without the assistance of a hearing aid, and to calculate the directivity index from the directional response. The gains obtained with a hearing aid are distinguished by whether the unaided manikin gain is included in (simulated real-ear aided gain) or subtracted from (simulated insertion gain) the aided gain.